native-app-performance

by steipete

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SKILL.md About

---
name: native-app-performance
description: Native macOS/iOS app performance profiling via xctrace/Time Profiler and CLI-only analysis of Instruments traces. Use when asked to profile, attach, record, or analyze Instruments .trace files, find hotspots, or optimize native app performance without opening Instruments UI.
---

# Native App Performance (CLI-only)

Goal: record Time Profiler via `xctrace`, extract samples, symbolicate, and propose hotspots without opening Instruments.

## Quick start (CLI)

1) Record Time Profiler (attach):

```bash
# Start app yourself, then attach
xcrun xctrace record --template 'Time Profiler' --time-limit 90s --output /tmp/App.trace --attach <pid>
```

2) Record Time Profiler (launch):

```bash
xcrun xctrace record --template 'Time Profiler' --time-limit 90s --output /tmp/App.trace --launch -- /path/App.app/Contents/MacOS/App
```

3) Extract time samples:

```bash
scripts/extract_time_samples.py --trace /tmp/App.trace --output /tmp/time-sample.xml
```

4) Get load address for symbolication:

```bash
# While app is running
vmmap <pid> | rg -m1 "__TEXT" -n
```

5) Symbolicate + rank hotspots:

```bash
scripts/top_hotspots.py --samples /tmp/time-sample.xml \
  --binary /path/App.app/Contents/MacOS/App \
  --load-address 0x100000000 --top 30
```

## Workflow notes

- Always confirm you’re profiling the correct binary (local build vs /Applications). Prefer direct binary path for `--launch`.
- Ensure you trigger the slow path during capture (menu open/close, refresh, etc.).
- If stacks are empty, capture longer or avoid idle sections.
- `xcrun xctrace help record` and `xcrun xctrace help export` show correct flags.

## Included scripts

- `scripts/record_time_profiler.sh`: record via attach or launch.
- `scripts/extract_time_samples.py`: export time-sample XML from a trace.
- `scripts/top_hotspots.py`: symbolicate and rank top app frames.

## Gotchas

- ASLR means you must use the runtime `__TEXT` load address from `vmmap`.
- If using a new build, update the `--binary` path; symbols must match the trace.
- CLI-only flow: no need to open Instruments if stacks are symbolicated via `atos`.

_meta.json Metadata

{
  "ownerId": "kn70pywhg0fyz996kpa8xj89s57yhv26",
  "publishedAt": 1767651991861,
  "slug": "native-app-performance",
  "version": "1.0.0"
}